<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8" />
    <title>Document</title>
    <script src='lib/webgl-utils.js'></script>
    <script src='lib/webgl-debug.js'></script>
    <script src='lib/cuon-utils.js'></script>
    <script src="lib/cuon-matrix.js"></script>
</head>
<body onload="main()">
<canvas id="mybox" width="500" height="500">
    请更换新版浏览器查看效果!
</canvas>
<script >
    let VSHADER_SOURCE=`
    attribute vec4 a_position;
    uniform mat4 u_modelMatrix;
    void main(){
        gl_Position=u_modelMatrix*a_position;
    }`;
    let FSHADER_SOURCE=
        `void main(){
            gl_FragColor=vec4(1.0,0.3,0.3,1.0);
            }
        `;
    let ANGLE_STEP=45.0;

    function main(){
        let canvas=document.getElementById('mybox')
        let gl=getWebGLContext(canvas)
        if(!initShaders(gl,VSHADER_SOURCE,FSHADER_SOURCE)){
            console.log('初始化shader失败');
            return;
        }
        let n=initVertexBuffers(gl)
        if(n<0){
            console.log('设置顶点位置失败')
            return;
        }
        gl.clearColor(0.0,0.0,0.0,1.0)
        let currentAngle=0.0;
        let modelMatrix=new Matrix4();
        let u_modelMatrix=gl.getUniformLocation(gl.program,'u_modelMatrix');
        let tick=function(){
            currentAngle=animate(currentAngle)
            draw(gl,n,currentAngle,modelMatrix,u_modelMatrix);
            requestAnimationFrame(tick);
        }
        tick();
        


    }

    function initVertexBuffers(gl){
        let vertices=new Float32Array([0.0,0.3,-0.3,0.0,0.3,0.0])
        let n=3;
        let vertexBuffer=gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER,vertexBuffer);
        gl.bufferData(gl.ARRAY_BUFFER,vertices,gl.STATIC_DRAW);
        let a_position=gl.getAttribLocation(gl.program,'a_position');
        gl.vertexAttribPointer(a_position,2,gl.FLOAT,false,0,0);
        gl.enableVertexAttribArray(a_position)
        return n;
    }
    //绘制三角形
    function draw(gl,n,currentAngle,modelMatrix,u_modelMatrix){
        modelMatrix.translate(0.3,0,0);
        modelMatrix.setRotate(currentAngle,0,0,1)
        gl.uniformMatrix4fv(u_modelMatrix,false,modelMatrix.elements);
        gl.clear(gl.COLOR_BUFFER_BIT);
        gl.drawArrays(gl.TRIANGLES,0,n);        
        
    }
    

    let last=Date.now()
    function animate(angle){
        let now=Date.now()
        let elapsed=now-last;
        last=now;
        let currentAngle=angle+ANGLE_STEP*elapsed/1000.0;
        return currentAngle%=360
        
    }


</script>

</body>
</html>